Three-terminal power device with high switching speed and manufacturing process

ABSTRACT

An embodiment of a power device having a first current-conduction terminal, a second current-conduction terminal, a control terminal receiving, in use, a control voltage of the power device, and a thyristor device and a first insulated-gate switch device connected in series between the first and the second conduction terminals; the first insulated-gate switch device has a gate terminal connected to the control terminal, and the thyristor device has a base terminal. The power device is further provided with: a second insulated-gate switch device, connected between the first current-conduction terminal and the base terminal of the thyristor device, and having a respective gate terminal connected to the control terminal; and a Zener diode, connected between the base terminal of the thyristor device and the second current-conduction terminal so as to enable extraction of current from the base terminal in a given operating condition.

PRIORITY CLAIM

The present application is a United States national phase applicationfiled pursuant to 35 USC §371 of International Patent Application SerialNo. PCT/IT2006/000372, entitled THREE-TERMINAL POWER DEVICE WITH HIGHSWITCHING SPEED AND MANUFACTURING PROCESS, filed May 18, 2006; whichapplication is incorporated herein by reference in its entirety.

TECHNICAL FIELD

An embodiment of the present invention relates to a three-terminal powerdevice, and in particular to a power device that can be used ashigh-voltage actuator.

BACKGROUND

As is known, in the last few years numerous power-actuator structureshave been proposed in an endeavor to achieve characteristics such as lowpower dissipation, both during conduction (on-state) and duringswitching, high input impedance and high switching speed. In particular,the trend has been to pass from bipolar transistors (having lowon-dissipation) and MOS transistors (having low dissipation duringswitching), to hybrid components that combine the advantages of bothtypes of transistor. Amongst these, components have been proposed—suchas IGBTs (Insulated-Gate Bipolar Transistors), MCTs (MOS-ControlledThyristors), and ESTs (Emitter Switched Thyristors)—which, in additionto reaching different levels of compromise between power dissipationduring the on-state and during switching, envisage driving via aninsulated-gate electrode.

Amongst the hybrid solutions proposed, the ones that have provenparticular advantageous, for example because they enable a high blockingvoltage (which is the maximum reverse voltage that the device canwithstand without undergoing breakdown), are those based uponthyristors, which have a reduced forward voltage drop during operation,and which are driven as MOSFETs, i.e., with a control voltage applied toan insulated gate. Belonging to said category are MCTs and ESTs, which,however, have a somewhat modest reverse-bias safe-operating area (RBSOA)and long turn-off times.

In order to solve said problems, in the patent application No.WO2004102671 filed on May 19, 2003 and incorporated by reference, apower device with high switching speed based upon a thyristor has beenproposed. In particular, said power device, designated by 1 in FIG. 1,comprises a thyristor 2 and a MOSFET 3 connected in series between twocurrent-conduction terminals 4, 5. The power device 1 also has a drivingterminal 6, which is connected to an insulated-gate electrode of theMOSFET 3 and receives a voltage for turning on or off the device, and afurther terminal 7 connected to the thyristor 2, for fast extraction ofcharges during the turn-off of the device. In this way, upon turn-off,no current tails occur, and turn-off is very rapid. In addition, thepower device does not have any parasitic components and so has a largeRBSOA.

Although advantageous for the aforesaid reason, the power device 1 has,however, the drawback of not being of a standard type, in so far as ithas four terminals (two control terminals and two current-conductionterminals), unlike the majority of power actuators, which have onlythree terminals (one control terminal and two current-conductionterminals).

SUMMARY

An embodiment of the present invention is a power device that willenable the above drawbacks to be overcome and that will constitute afurther improvement of power devices of a known type.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the subject matter discussed herein, oneor more embodiments thereof are now described, purely by way ofnon-limiting example and with reference to the attached drawings,wherein:

FIG. 1 shows a circuit diagram of a power device of a known type;

FIG. 2 shows a circuit diagram of a power device according to anembodiment of the present invention;

FIG. 3 shows a cross section through an elementary structure of thepower device of FIG. 2;

FIGS. 4-8 show cross sections through a wafer of semiconductor material,in successive manufacturing steps of the power device of FIG. 3;

FIG. 9 shows a cross section through an end portion of the power deviceof FIG. 2, integrating a Zener diode thereof; and

FIGS. 10 and 11 show equivalent electrical circuit diagrams of the powerdevice of FIG. 2 in two different operating conditions, respectively aturn-on and a turn-off condition.

DETAILED DESCRIPTION

As shown in the equivalent electrical diagram of FIG. 2, a power device10 according to an embodiment of the present invention has threeterminals, and in particular a first current-conduction terminal A(anode), a second current-conduction terminal K (cathode), and a controlterminal G (gate) for supplying a turn-on/turn-off voltage to thedevice.

The power device 10 comprises a thyristor 12 (in particular, a siliconcontrolled rectifier—SCR), and a first insulated-gate switch device 14(in particular a MOS transistor), connected in series between the firstand second current-conduction terminals A, K. In detail, the thyristor12 has its anode connected to the first current-conduction terminal A,its cathode connected to a first internal node 15, and its baseconnected to a second internal node 16. The first insulated-gate switchdevice 14 is connected between the first internal node 15 and the secondcurrent-conduction terminal K, and has its gate terminal connected tothe control terminal G of the power device 10.

The power device 10 further comprises: a second insulated-gate switchdevice 18 (in particular a high-voltage IGBT), which is connectedbetween the first current-conduction terminal A and the second internalnode 16 and has its gate terminal which is also connected to the controlterminal G, and hence is connected to the gate terminal of the firstinsulated-gate switch device 14; and a Zener diode 19, which isconnected between the second internal node 16 and the secondcurrent-conduction terminal K and in particular has its anode connectedto the second current-conduction terminal and its cathode connected tothe second internal node 16.

FIG. 3 shows a cross section of an embodiment of an elementary structureof the power device 10, provided as monolithic structure integrated in asingle body of semiconductor material 20. The power device 10 maycomprise in general a plurality of elementary structures arrangedalongside one another, extending parallel to one another for example ina horizontal direction orthogonal to the vertical section of FIG. 3, andeach elementary structure may comprise one or more elementary cells. Inthe illustrated embodiment, the elementary structure comprises oneelementary cell.

In detail, the body of semiconductor material 20 has a bottom surface 20a and a top surface 20 b and comprises: a substrate 22, of a P⁺ type; abuffer layer 23, of an N⁺ type, which is arranged on the substrate 22and has the function of increasing, in a per-se known manner, thebreakdown voltage of the device; a first base region, referred tohereinafter as drift region 24, of an N⁻ type, arranged on the bufferlayer 23; a second base region, referred to hereinafter as base region26, of a P type, housed within the drift region 24; a cathode region 27,of an N type, arranged on the base region 26; and an epitaxial region28, of an N⁻ type. The epitaxial region 28 houses: first well regions30, of a P⁺ type, set partially in contact with the base region 26;second well regions 32, of an N⁺ type, set in contact with the cathoderegion 27 and arranged beside and internally to the first well regions30; first body regions 33, of a P type, housing first source regions 34,of an N⁺ type, and arranged internally to the second well regions 32;and second body regions 35, of a P type, housing second source regions36, of an N⁺ type, and arranged externally to, and in contact with, thefirst well regions 30.

In greater detail, the bottom surface 20 a of the power device 1,defined by the substrate 22, is covered by a metal layer 38 connected tothe first current-conduction terminal A, accessible from outside thepower device 10. The drift region 24 is formed by a layer not accessiblefrom outside, grown epitaxially, as explained in greater detailhereinafter, the characteristics (in terms of thickness and resistivity)of which depend upon the voltage class of the power device 10. The baseregion 26 is a buried region, connected to the top surface 20 b via thefirst well regions 30, which extend through the epitaxial region 28between the top surface 20 b and the base region 26. The cathode region27 is a buried region, connected to the top surface 20 b via the secondwell regions 32, which extend through the epitaxial region 28 betweenthe top surface 20 b and the cathode region 27, and is delimitedlaterally by the first well regions 30, without necessarily beingcontiguous thereto. The epitaxial region 28 may have the sameresistivity as the drift region 24, but a smaller thickness. The firstbody regions 33 are housed within the epitaxial region 28 and aredelimited laterally by the second well regions 32. In the exampleillustrated, the first body regions 33 house two first source regions34, similarly to what is known in the technology of vertical-conductionMOSFET power devices. In particular, the presence of the second wellregions 32 inhibits the lateral parasitic transistors that could beformed between the first well regions 30, the epitaxial region 28 andthe first body regions 33. Also the second body regions 35 are housedwithin the epitaxial region 28 laterally in contact with the first wellregions 30. In the example illustrated, the second body regions 35 eachhouse a second source region 36.

Above the top surface 20 b, the power device 10 comprises firstinsulated-gate regions 39, including in a known way an electrode, forexample of polycrystalline silicon, surrounded by a dielectric layer,for example of silicon oxide. The respective electrodes of the firstinsulated-gate regions 39 are connected to one another and to thecontrol terminal G of the power device 10 (as shown schematically),accessible from outside. In the example illustrated, two first gateregions 39 are present adjacent to one another, extending, in a per-seknown manner, above the portions of the first body regions 33 setbetween the first source regions 34 and the epitaxial region 28, andalso partially above the epitaxial region 28 and the first sourceregions 34. In a substantially similar way, the power device 10comprises second insulated-gate regions 40, the electrodes of which arealso connected to one another and to the control terminal G of the powerdevice 10. In the example illustrated, two second insulated-gate regions40 are present, extending, in a per-se known manner, above the portionsof the second body regions 35 set between the second source regions 36and the epitaxial region 28, and also partially above the epitaxialregion 28 and the second source regions 36.

The power device 10 further comprises: a cathode metallization 42extending on the top surface 20 b between the first insulated-gateregions 39, in contact with the first body regions 33 and source regions34, and connected to the second current-conduction terminal K of thepower device 10, accessible from outside; and a floating metallization44, which is also set on the top surface 20 b between respective firstand second insulated-gate regions 39, 40, in contact with the secondbody and source regions 35, 36 and with the first well regions 30, andconnected to the second internal node 16 (FIG. 2) of the power device10. The floating metallization 44 consequently short-circuits the secondsource regions 36 and the first well regions 30 adjacent thereto.

Basically, the thyristor 12 is formed by the substrate 22 (anode), thebuffer layer 23 (which may not be present) and the drift region 24(first base), the base region 26 (second base, base terminal accessiblefrom outside), and the cathode region 27 (cathode). The firstinsulated-gate switch device 14 (MOS transistor) is formed by thecathode region 27 (drain), the epitaxial region 28 and the first bodyregions 33 (channel), the first source regions 34 (source) and the firstinsulated-gate regions 39 (gate). The second insulated-gate switchdevice (IGBT) 18 is formed by the substrate 22 (collector), the driftregion 24, the epitaxial region 28 and the second body regions 35(channel), the second source regions 36 (emitter), and the secondinsulated-gate regions 40 (gate).

The Zener diode 19 (not shown in the cross section of FIG. 3) can beintegrated in the body of semiconductor material 20 using any knowntechnique, for example in the way which will be described in detailhereinafter. In particular, the junction of the Zener diode 19 may beprovided by the layers and regions already formed for obtaining thevarious components described, with an appropriate layout of the powerdevice.

The power device 10 may be manufactured using traditional manufacturingtechniques of silicon devices, for example, in the way describedhereinafter with reference to FIGS. 4 to 9.

Initially (FIG. 4), the buffer layer 23 and then the drift region 24 aregrown epitaxially on the substrate 22; the buffer layer 23 has a reducedthickness (for example, 5-20 μm) and a low resistivity (for example, 1-5Ω·cm), and the drift region 24 has a larger thickness and higherresistivity (determined principally on the basis of the voltage ratingof the device—BV_(AK)). The epitaxial growth may be performed in asingle step, or alternatively, through successive growth steps.

Next (FIG. 5), using an appropriate phototechnique, an implantation ofdopant of a P type (for example boron atoms) is carried out followed bya corresponding diffusion to form the base region 26; then, by means ofa further phototechnique, an implantation of dopant of an N type (forexample As, Sb or P, or a combination thereof) and correspondingdiffusion is carried out to form the cathode region 27 within the baseregion 26. In particular, the cathode region 27 has a smaller width thanthe base region 26, to enable formation of the first well regions 30laterally to the cathode region 27.

A further epitaxial growth is then carried out to form the epitaxiallayer 28 (FIG. 6). The epitaxial layer 28, of an N⁻ type, has aresistivity similar to that of the drift region 24, but a smallerthickness (for example, approximately 5 μm). As shown in FIG. 6, thefurther epitaxial growth leads to an increase in the thickness of thecathode region 27, which thus extends in part within the epitaxial layer28.

Next (FIG. 7), the first well regions 30, of a P type, reaching the baseregion 26, and the second well regions 32, of an N type, reaching thecathode region 27, are implanted and diffused. In a per-se known manner,also a ring of an edge structure (for example of a <<SIPS>> or <<VLD>>type) of the device may be provided.

The process is then completed by providing the body and source regionsof the first and second insulated-gate switch devices 14, 18, usingstandard process steps for manufacturing of vertical-flow DMOSstructures. The respective body and source regions, and the respectivegate regions and contacts, may be formed simultaneously with the sameprocess steps.

FIG. 9 shows a dedicated portion of the power device 10 (in particular,an end portion thereof), in which the Zener diode 19 is provided, in away substantially similar to what is described in the European patentapplication No. EP 05425492.5 filed on Jul. 8, 2005, which isincorporated by reference. As it is clear from FIG. 9, the Zener diode19 is provided without adding any further regions with respect to themanufacturing process of the power-device elementary structure, inparticular exploiting the P⁺ and N⁺ well implants and diffusions alreadypresent. In detail, the Zener diode 19 is a lateral bipolar transistorwith open base having as emitter the first well region 30, of a P⁺ type(connected to the second internal node 16 via the floating metallization44), as base a first additional well 46 of an N⁺ type (may be formedsimultaneously with the first well regions 30), and as collector asecond additional well 48 of a P⁺ type (may be formed simultaneouslywith the second well regions 32), which is electrically connected, via adiode metallization 49 arranged above the second surface 20 b, to thesecond current-conduction terminal K. The Zener voltage of the Zenerdiode 19 is the BV_(ceo) voltage of said lateral transistor.

Operation of the power device 10 is now described also with reference toFIGS. 10 and 11, in which, for simplicity of illustration, the first andsecond insulated-gate switch devices 14, 18 are modelled as twoswitches, in the closed and open operating conditions, respectively.

In particular, the first insulated-gate switch device 14, set in serieswith the cathode of the thyristor 12, has a current-cutting function,i.e., it enables or blocks passage of current through the thyristor. Thesecond insulated-gate switch device 18, set between the anode and thebase of the thyristor 12, has, instead, the function of enablingturning-on thereof. Since the aforesaid switch devices are of the sametype (with an N channel) and have the gate terminal in common, when thecontrol voltage (designated by V_(GATE)) exceeds a threshold voltage(designated by V_(TH)), as shown in FIG. 10, they are both conducting(closed switches), thus enabling the passage of a current in thethyristor 12. Instead, when the control voltage V_(GATE) is below thethreshold voltage V_(TH), as shown in FIG. 11, the two switches open,interrupting the current flow in the thyristor 12.

In detail, in an example of use the first current-conduction terminal Ais set at a high positive voltage, whilst the second current-conductionterminal K is set at a reference voltage (ground) so that the anodeterminal A is at a higher voltage than the cathode K.

When V_(GATE) is greater than V_(TH), a certain current flows throughthe second insulated-gate switch device 18, and precisely from itscollector region (substrate 22) towards its emitter region (secondsource region 36). Since the second source region 36 is connected, viathe floating metallization 44, to the first well region 30, theaforesaid current reaches the base region 26 of the thyristor 12. Saidcurrent, even though it is not particularly high, is in any casesufficient to trigger the thyristor 12 (in a way similar to traditionalthyristors, the triggering current depends upon the common-base gain ofthe PNP and NPN transistors forming the thyristor), which, once it hasbeen turned on, does not require a further modulation of the drivingcurrent. Turn-on of the device causes a flow of current (designated byI_(on)) from the first current-conduction terminal A to the secondcurrent-conduction terminal K. In the turn-on state, the voltage dropbetween said terminals is due substantially to the voltage drop acrossthe thyristor 12 (the voltage drop across the first switch device 14 isin fact negligible in so far as it is a low-voltage MOSFET), and is verylow. It should be noted that in this situation, the Zener diode 19(having a non-zero voltage across it, for example higher than 2 V)prevents a direct passage of current between the firstcurrent-conduction terminal A and the second current-conduction terminalK that would not enable turn-on of the thyristor 12.

When, instead, V_(GATE) is lower than V_(TH), the first insulated-gateswitch device 14 and the second insulated-gate switch device 18 switchoff substantially simultaneously, causing turn-off of the power device10. During the turn-off phase, all the current coming from the firstcurrent-conduction terminal A (designated by I_(off)), since it cannotcirculate in the two switches, is diverted into the base of thethyristor 12, and then, through the Zener diode 19, towards the secondcurrent-conduction terminal K. In this way, turn-off of the device isextremely fast (in the region of some hundreds of nanoseconds), withoutany current tail typical of bipolar-conduction actuator devices of aknown type. In fact, all the charges stored in the base regions of thetwo PNP and NPN transistors forming the thyristor 12 (drift region 24and base region 26), are forcibly removed, and consequently the anodecurrent drops rapidly to zero. The Zener diode 19 hence enables aselective passage of current between the second internal node 16 and thesecond current-conduction terminal K, preventing passage of currentduring the on-phase of the thyristor 12, and enabling said passage ofcurrent only during the turn-off phase of the thyristor.

Advantages of the power device and of the corresponding manufacturingprocess according to one or more embodiments of the invention areevident from the above description.

In particular, the structure of the device enables a high currentdensity to be obtained, thanks to the presence of a thyristor, and ahigh switching speed, thanks to the cascode configuration between athyristor and a MOSFET, with a fast removal by extraction of the basecharges during turn-off.

In addition, the device has only three terminals (two current-conductionterminals and one control terminal), and is consequently of a “standard”type, easily integrable in traditional technologies.

The power device may not have any parasitic components, so that it mayhave both a large FBSOA (Forward-Bias Safe-Operating Area) and a largeRBSOA.

Basically, the device is a power actuator that is particularly suitablefor all those circuit applications in which a high reverse-bias blockingcapacity (greater than 1 kV) and a high operating frequency (up to 100kHz) are required.

Finally, it is clear that modifications and variations can be made towhat is described and illustrated herein, without thereby departing fromthe scope of the subject matter disclosed herein.

For example, the charge-extraction terminal in the turn-off phase(second internal node 16) to which the cathode of the Zener diode 19 isconnected could be connected to another base region of the thyristor 12,in particular to the drift region 24.

In addition, although the vertical structure described in FIG. 3 mayextend horizontally in strips with an alternation of strips associatedwith the first insulated-gate switch device 14 and of strips associatedwith the second insulated-gate switch device 18, it is evident that alsoother layouts, of a known type, are equally possible.

The power device 10 may form part of a system in which the power deviceis coupled to circuitry that is disposed on a same die as the powerdevice, or that is disposed on a different die from the power device.

1. A power device, comprising: a first current-conduction terminal; a second current-conduction terminal; a control terminal configured to receive a control voltage of said power device; and a thyristor device and a first insulated-gate switch device connected in series between said first and second current-conduction terminal, said first insulated-gate switch device having a gate terminal connected to said control terminal, and said thyristor device having a base terminal, and a second insulated-gate switch device connected between said first current-conduction terminal and said base terminal of said thyristor device, and having a respective gate terminal connected to said control terminal.
 2. The device according to claim 1, wherein said first insulated-gate switch device is a MOSFET, and said second insulated-gate switch device is an IGBT.
 3. The device according to claim 2, wherein said MOSFET has its drain terminal connected to said thyristor device and its source terminal connected to said second current-conduction terminal, and said IGBT has its collector terminal connected to said first current-conduction terminal and its emitter terminal connected to said base terminal of said thyristor device, said MOSFET and said IGBT having respective channels with the same type of conductivity.
 4. The device according to claim 1, further comprising a selective-current-conduction element connected between said base terminal of said thyristor device and said second current-conduction terminal, and configured to enable extraction of current from said base terminal of said thyristor device towards said second current-conduction terminal in a given operating condition of said first and second insulated-gate switch devices.
 5. The device according to claim 4, wherein said selective-current-conduction element is a Zener diode, in particular having its anode terminal connected to said second current-conduction terminal and its cathode terminal connected to said base terminal of said thyristor device.
 6. The device according to claim 1, comprising a body of semiconductor material having a first surface and a second surface and including: a substrate region having a first type of conductivity and defining said first surface; a first base region having a second type of conductivity and set on said substrate region; a second base region having said first type of conductivity, and housed at least partially in said first base region; a first conductive region having said second type of conductivity, set on said second base regional and defining said second surface; a second conductive region having said second type of conductivity, separated from said first conductive region by a first channel region having said first type of conductivity; a third conductive region having said second type of conductivity and being separated from said first conductive region by a second channel region having said first type of conductivity; and a first well region having said first type of conductivity and extending from said second surface to one of said first and second base regions, said second and third conductive regions being arranged laterally and on opposite sides with respect to said first well regional, and said second channel region being in contact with said first well region.
 7. The device according to claim 6, wherein the gate terminals of said first and second insulated-gate switch device comprise respective gate electrodes set above, and electrically insulated from, said second surface of said body of semiconductor material and overlying respectively said first and second channel regions; said gate electrodes being connected to one another and to said control terminal, said first current-conduction terminal being connected to said substrate region, said second current-conduction terminal being connected to said second conductive region, and said base terminal of said thyristor device being connected to a floating conductive region set on said second surface, in contact with said third conductive region and said first well region.
 8. The device according to claim 6, wherein said first conductive region is formed by a buried region overlying said second base region and by an epitaxial region overlying said buried region; and wherein said body of semiconductor material further comprises a second well region having said second type of conductivity and extending from said second surface to said buried region through said epitaxial region; said epitaxial region housing a first body region and a second body region defining said first and second channel regions and in turn housing said second and third conductive regions, and said first body region being delimited laterally by said second well region.
 9. The device according to claim 4, comprising a body of semiconductor material having a first surface and a second surface and including: a substrate region having a first type of conductivity and defining said first surface; a first base region having a second type of conductivity and set on said substrate region; a second base region having said first type of conductivity, and housed at least partially in said first base region; a first conductive region having said second type of conductivity, set on said second base region and defining said second surface; a second conductive region having said second type of conductivity, separated from said first conductive region by a first channel region having said first type of conductivity; a third conductive region having said second type of conductivity and being separated from said first conductive region by a second channel region having said first type of conductivity; a first well region having said first type of conductivity and extending from said second surface to one of said first and second base regions, said second and third conductive regions being arranged laterally and on opposite sides with respect to said first well region, and said second channel region being in contact with said first well region; and wherein said first conductive region is formed by a buried region overlying said second base region and by an epitaxial region overlying said buried region; and wherein said body of semiconductor material further comprises, at a diode portion thereof, a third well region having said second type of conductivity and extending through said epitaxial region laterally with respect to said first well region, and a fourth well region having said first type of conductivity and extending through said epitaxial region laterally in contact with said third well region; said first, second and third well regions defining together said selective current-conduction element, and a contact region, arranged on said second surface, electrically connecting said third well region to said second current-conduction terminal.
 10. A process for manufacturing a power device, comprising: providing a body of semiconductor material having a first surface and a second surface; forming a first current-conduction terminal above said first surface, and a second current-conduction terminal and a control terminal above said second surface; forming, in said body of semiconductor material, a thyristor device and a first insulated-gate switch device connected in series between said first and said second current-conduction terminals, said first insulated-gate switch device having a gate terminal connected to said control terminal, and said thyristor device having a base terminal, and forming, in said body of semiconductor material, a second insulated-gate switch device connected between said first current-conduction terminal and said base terminal of said thyristor device and having a respective gate terminal connected to said control terminal.
 11. The process according to claim 10, further comprising forming, in said body of semiconductor material, a selective current-conduction element connected between said base terminal of said thyristor device and said second current-conduction terminal, and configured to enable extraction of current from said base terminal of said thyristor device towards said second current-conduction terminal in a given operating condition of said first and second insulated-gate switch devices.
 12. The process according to claim 11, wherein said selective current-conduction element is a Zener diode, in particular having its anode terminal connected to said second current-conduction terminal and its cathode terminal connected to said base terminal of said thyristor device; and wherein said first insulated-gate switch device is a MOSFET, and said second insulated-gate switch device is an IGBT, said MOSFET and IGBT having respective channels with the same type of conductivity.
 13. The process according to claim 10, comprising: providing a substrate of a first type of conductivity and defining said first surface; forming a first base region of a second type of conductivity, on said substrate; forming a second base region of said first type of conductivity in said first base region; forming a first conductive region of said second type of conductivity on said second base region, said first conductive region defining said second surface; forming a first well region of said first type of conductivity, extending from said top surface as far as one of said first and second base regions; forming a second conductive regional having said second type of conductivity, separated from said first conductive region by a first channel region having said first type of conductivity; and forming a third conductive region having said second type of conductivity and separated from said first conductive region by a second channel region having said first type of conductivity, said second and third conductive regions being set laterally and on opposite sides with respect to said first well region, and said second channel region being in contact with said first well region.
 14. The process according to claim 13, further comprising: forming a first gate electrode and a second gate electrode above, and electrically insulated from, said second surface of said body of semiconductor material and overlying respectively said first and second channel regions; connecting said gate electrodes to one another and to said control terminal; forming a floating conductive region on said second surface in contact with said third conductive region and said first well region; and connecting said first current-conduction terminal to said substrate region, said second current-conduction terminal to said second conductive region, and said base terminal of said thyristor device to said floating conductive region.
 15. The process according to claim 11, comprising: providing a substrate of a first type of conductivity and defining said first surface; forming a first base region of a second type of conductivity, on said substrate; forming a second base region of said first type of conductivity in said first base region; forming a first conductive region of said second type of conductivity on said second base region, said first conductive region defining said second surface; forming a first well region of said first type of conductivity, extending from said top surface as far as one of said first and second base regions; forming a second conductive region having said second type of conductivity, separated from said first conductive region by a first channel region having said first type of conductivity; and forming a third conductive region having said second type of conductivity and separated from said first conductive region by a second channel region having said first type of conductivity, said second and third conductive regions being set laterally and on opposite sides with respect to said first well region, and said second channel region being in contact with said first well region; and, wherein forming said first conductive region comprises forming a buried region overlying said second base region, and growing an epitaxial region on said buried region; further comprising: forming, at a diode portion of said body of semiconductor material, a third well region having said second type of conductivity and extending through said epitaxial region laterally with respect to said first well region, and a fourth well region having said first type of conductivity and extending through said epitaxial region laterally in contact with said third well region, said first, second and third well regions defining together said selective current-conduction element; and forming a contact region on said second surface, electrically connecting said third well region to said second current-conduction terminal.
 16. An electronic device, comprising: a first terminal; a second terminal; a control terminal; a first switch having a first node coupled to the first terminal, a second node, and a trigger node; a trigger having a first node coupled to the first terminal, a second node coupled to the trigger node of the switch, and a control node coupled to the control terminal; and a second switch having a first node coupled to the second node of the first switch, a second node coupled to the second terminal, and a control node coupled to the control terminal.
 17. The electronic device of claim 16 wherein the first switch comprises a thyristor.
 18. The electronic device of claim 16 wherein the first switch comprises a silicon-controlled rectifier.
 19. The electronic device of claim 16, wherein the trigger comprises a transistor.
 20. The electronic device of claim 16, wherein the trigger comprises an insulated-gate transistor.
 21. The electronic device of claim 16, wherein the trigger comprises an insulated-gate bipolar transistor.
 22. The electronic device of claim 16, wherein the second switch comprises a transistor.
 23. The electronic device of claim 16, wherein the second switch comprises an insulated-gate transistor.
 24. The electronic device of claim 16, further comprising a discharger having a first node coupled to the trigger node of the first switch and a second node coupled to the second terminal.
 25. The electronic device of claim 16, further comprising a diode coupled between the trigger node of the first switch and the second terminal.
 26. The electronic device of claim 16, further comprising a Zener diode having a cathode coupled to the trigger node of the first switch and having an anode coupled to the second terminal.
 27. The electronic device of claim 16 wherein the trigger node of the first switch is coupled to the second terminal.
 28. The electronic device of claim 16, further comprising a discharger having a first node coupled to the trigger node of the first switch and a second node coupled to the control terminal.
 29. An electronic device, comprising: a first terminal; a second terminal; a control terminal; a first switch having a first node coupled to the first terminal, a second node, and a trigger node; a discharger having a first node coupled to the trigger node of the switch; and a second switch having a first node coupled to the second node of the first switch, a second node coupled to the second terminal, and a control node coupled to the control terminal.
 30. The electronic device of claim 29 wherein the first switch comprises a thyristor.
 31. The electronic device of claim 29 wherein the second switch comprises a transistor.
 32. The electronic device of claim 29 wherein the discharger has a second node coupled to the second terminal.
 33. The electronic device of claim 29 wherein the discharger has a second node coupled to the control terminal.
 34. The electronic device of claim 29 wherein the discharger comprises a diode.
 35. The electronic device of claim 29 wherein the discharger comprises a Zener diode.
 36. The electronic device of claim 29 wherein the trigger node is coupled to the first terminal.
 37. A system, comprising: a load; and an electronic device coupled to the load and including a first terminal, a second terminal, a control terminal, a first switch having a first node coupled to the first terminal, a second node, and a trigger node, a trigger having a first node coupled to the first terminal, a second node coupled to the trigger node of the switch, and a control node coupled to the control terminal, and a second switch having a first node coupled to the second node of the first switch, a second node coupled to the second terminal, and a control node coupled to the control terminal.
 38. The system of claim 37 wherein the load and the electronic device are disposed on a same integrated circuit.
 39. The system of claim 37 wherein the load and the electronic device are disposed on respective integrated circuits.
 40. The system of claim 37 wherein the load is coupled to the first terminal of the electronic device.
 41. The system of claim 37 wherein the load is coupled to the second terminal of the electronic device.
 42. A system, comprising: a load; and an electronic device coupled to the load and including a first terminal, a second terminal, a control terminal, a first switch having a first node coupled to the first terminal, a second node, and a trigger node, a discharger having a first node coupled to the trigger node of the switch, and a second switch having a first node coupled to the second node of the first switch, a second node coupled to the second terminal, and a control node coupled to the control terminal.
 43. The system of claim 42 wherein the load and the electronic device are disposed on a same integrated circuit.
 44. The system of claim 42 wherein the load and the electronic device are disposed on respective integrated circuits.
 45. The system of claim 42 wherein the load is coupled to the first terminal of the electronic device.
 46. The system of claim 42 wherein the load is coupled to the second terminal of the electronic device.
 47. A method, comprising: generating a triggering signal in response to a control signal having a first state; triggering a thyristor to conduct a current with the triggering signal; closing a switch that is serially coupled to the thyristor in response to the control signal having the first state; and opening the switch in response to the control signal having a second state.
 48. The method of claim 47 wherein generating the triggering signal comprises generating the triggering signal with an insulated-gate bipolar transistor.
 49. The method of claim 47, further comprising discharging the thyristor in response to the control signal having the second state.
 50. A method, comprising: discharging a thryistor in response to a control signal having a first state; opening a switch that is serially coupled to the thyristor in response to the control signal having the first state; and closing the switch in response to the control signal having a second state.
 51. The method of claim 50 wherein discharging the thyristor comprises discharging the thyristor with a Zener diode.
 52. The method of claim 50, further comprising triggering the thyristor to conduct a current in response to the control signal having the second state. 